Headlights and Cruise not working

Hi Wilson I just happen to be looking at the gen II schematics for another person so I will find your problem also

Locate and check 40A HEAD fuse. This Fuse supplies power through H-LP relay contacts and then through hi lo relay contacts.

40 amp fuse is blown or the relay contacts are bad at H-LP (head light power) relay. Relay is energized from body ecu (problem is not likely here).

This fuse and relay are under the hood (engine compartment).

Are you running any after market headlights that could be pulling more than 40 amps?

 

Also after the power passes through h-lp relay it goes the the DIM relay which is also under the hood and very interesting think I will note is that each headlight filiment has its own 10 amp fuse located under the hood right next to the h-lp and dim relays..
So 4 fuses here each 10 amp. 2 fuses for right side high and low beams and 2 fuses for left side high and low beams..
I dought your could have blown all 4 fuses here so problem is back at 40A HEAD FUSE..or H-LP relay.

I don't know how this could be related to cruse control.

Hope all this helps Wilson...

 

btw, your 12v either needs to be charged or replaced.

 

If you really think the headlight and cruse control are related..
I would recomend a full prius systems reboot ... Whereby you disconnect negative battery terminal connection for 3 or 4 minutes.

This would reset all ecu's computers..which I allways recomend after having dead 12 volt battery and jump start (not sure if you have had a jump lately)..

Something you could do very carefully remove h-lp relay cover. But inserting relay back into socket could damage relay pressing to hard to insert it. and trying to remove it without cover would surely damage it with to much force and nothing to grab onto.

with relay cover off and intalled you could manually activate it by squeezing contacts... If youve never opened a relay before I wouldn't want you to start now...and I heard that 3 dollar relay costs 75 dollars from toyota ...

I think I would recomend total prius system reset..

by disconnecting 12 volt battery you will loose learned fuel trim memory. which will take about 200 miles of driving to relearning of fuel trims
and loose radio presets, a and b trip mileage counts.. and driverside auto window up setting... just lower window half way pull and hold up window switch 1 second longer after window fully closes and window motor controll will be reprogrammed..

 

another Idea if you have another person you could listen for h-lp relay to click on while someone else turns on the headlight switch.
if relay clicks on but no headlights its definately relay contacts are burnt.. and could possibly be cleaned/sanded by opening relay . Sanding relay contacts only last a short time maybe a month..
Do not sand contacts if they visually look ok. If you start sanding good relay contacts you shorted its life to only a month or so..

but if relay doesn't click when another person turns on the headlights then the body ecu is unable to activate relay... and possibly body ecu is not reading cruse controll request... You then have to do a prius reboot/.reset/restart by disconnecting 12volt battery temporily..

 

i don't know that they are related either, but a new battery is 13+ and below 12.4 or 5 is marginal. one day, the car won't start.

 

i doubt it, but it needs attending anyway, so you might was well eliminate the possibility. how old is it?

 

Try and make sure which relay your are hearing. buy turning on headlights could be hearing only dim relay click. check that both relays click independantly.. turn on headlights. toggle hi low switch. dim relay should click. verify only low beams are on by dash board indicator.This is the dim relay deenergized position now very h-lp relay clicks.. If powering on the headlights in high beam mode both relays click on simotaniously. power on headlights in low beam mode and then you will be able to tell for sure if h-lp relay is clicking on..

 

50-50.

 

If your are positive you are seeing 12 volts switched on and off through h-lp relay you should have voltage at either the 10 amp low beam fuses or the 10amp high beam fuses depending on which mode your in hi or low beam.

there are 4 fuses near the h-lp and dim relays one for each of the four filiments... If you see voltage at those fuses then you should have voltage at the headlight filiments..

your meter might show voltage at the fuse with no headlight load (disconnected headlight from absent fuse) try and force a very small guage wire into inserted fuse socket. then check for voltage with headlight load applied through fuse..

voltage could pass through burnt relay contacts to meter without headlights being connected through the fuses.

but with headlights connected through fuses is there still 12 volts present... under load burnt contacts will not pass voltage..

 

see my last 2 paragraphs first for simple trouble shooting.

determine at the four 10 amp fuses.
A. the 12 volt supply side of the fuses and
B. the headlight filiment side of the fuses.
hopefull all voltages are on the same side of all fuses..
and hopefully all filiments are on the other side of all four fuses..

to verfy that other side of the filliments are grounded and not open (and everthing turned off) you can jumper 12 volts from the jump start terminal (upper left hand corner under red cover) to each filliment side of the fuse (all four fuses removed). illuminating each of the 4 headlights indivdually..

If the four beams light up then were are back to the relay contacts..

And I never considered the dim relay could be the problem till now..

my prius wireing diagram shows pins 1 thru 5 on the dim relay and pins 1,2,3,5 of the h-lp relay..
if these are labled on the socket or the relay that you can read. you can simply jumper across the socket and test head lights and wireling.
jumper h-lp relay pins 3 to 5 with fuses in and everything turned off. low beams should turn on
If low beams dont light up you will then need to jumper pin 3 to 5 of the dim relay with h-lp still jumpered headlight will light then..

if not go to the begining of the post for more trouble shooting..
I'm going to pull my relays an see if i can read the pin numbers.
12 volts comes in pin 5 of h-lp relay and switches out pin 3 of h-lp relay then goes to pin3 of dim relay and ( crap the diagram is wrong it shows that 12 volts can never reach the low beams so the obvious is)
pin 4 goes to the low beams pin 5 to the high beams..

nope socket connections not numbered and relay pins not numbered...I removed cover from dim relay. contacts burried deep within relay. contacts not accessible for cleaning. contacts cannot be manually squeezed to activate. my contacts look clean I have 76000 miles on mine.

 

Hi wilson your assumption is good..
I put out a new post "simplified headlight trouble shooting for gen II prius"
It simplifies things tremendously doesn't even require volt meter..
You could read voltage at headlight socket and still have bad relay contacts.. A volt meter will only require a micro-amp( .000001 amp) to show a good voltage reading. where the relay contacts will have to pass 6,000,000 micro amps to light a single beam.
volt meter can be misleading to the seasoned/experienced technician..

Bad relay contacts can easily pass a few micro-amps and show good voltage with a meter.
But bad relay contacts will not pass the 6,000,000 micro-amps needed to supply 12 volts to a single headlight beam..